Method and apparatus for a refrigeration circuit

ABSTRACT

A method and apparatus for a refrigeration circuit is disclosed. In the refrigeration circuit, a single-component or multi-component refrigerant, preferably a nitrogenous refrigerant, in particular nitrogen, circulates, where at least one partial stream of the refrigerant is expanded. The expansion of the refrigerant takes place in at least two expansion turbines that are arranged in series, and the temperature of the refrigerant at the exit of the expansion turbines, or at least at one of the exits of the expansion turbines, is above the saturation temperature of the refrigerant. In this connection, the temperature of the refrigerant at the exit of the expansion turbines, or at least at one of the exits of the expansion turbines, is less than 10° C., preferably less than 5° C., in particular less than 2° C., above the saturation temperature of the refrigerant.

This application claims the priority of German Patent Document No. 10 2007 005 098.6, filed Feb. 1, 2007, the disclosure of which is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method and apparatus for a refrigeration circuit, in which a single-component or multi-component refrigerant, preferably a nitrogenous refrigerant, in particular nitrogen, circulates, wherein at least one partial stream of the refrigerant is expanded.

Generic methods for operating refrigeration circuits are sufficiently known from the prior art. In these types of refrigeration circuits, isothermal refrigerating capacity is generated by means of the evaporation of the single-component or multi-component refrigerant. To this end, the single-component or multi-component refrigerant is expanded in an expansion turbine. However, until now only one expansion turbine has been used in these types of refrigeration circuits. However, when only one turbine is used, it cannot be avoided that a substantial portion of the refrigerating capacity of this expansion turbine occurs above the condensation temperature of the to-be-expanded refrigerant, and cannot be used as a result.

The objective of the present invention is disclosing a generic method and apparatus for operating a refrigeration circuit that avoids the aforementioned disadvantages, but, in particular, makes possible the realization of a refrigeration circuit with a degree of efficiency that is higher, as compared with comparable refrigeration circuits.

A generic method and apparatus for operating a refrigeration circuit is provided to attain this objective, which is characterized in that the expansion of the refrigerant takes place in at least two expansion turbines that are arranged in series, and the temperature of the refrigerant at the exit of the expansion turbines or at least at one of the exits of the expansion turbines is above the saturation temperature of the refrigerant.

Based on the fact that, in the case of the inventive method and apparatus for operating a refrigeration circuit, a considerably greater (as compared to prior art methods) portion of the refrigerating capacity of the expansion turbines occurs below the condensation temperature of the single-component or multi-component refrigerant being used, this capacity can be used for condensation. The result of this is a considerable increase in the efficiency of the inventive method for operating a refrigeration circuit. If the refrigerating capacity were to be generated above the condensation temperature, this capacity could only be released unused to the environment.

Additional advantageous embodiments of the inventive method and apparatus for operating a refrigeration circuit are characterized in that:

the temperature of the refrigerant at the exits of the expansion turbines, or at least at one of the exits of the expansion turbines, is less than 10° C., preferably less than 5° C., in particular less than 2° C., above the saturation temperature of the refrigerant;

the temperature of the refrigerant at the exits of all the expansion turbines is above the saturation temperature of the refrigerant; and

the exit side of the first expansion turbine can be connected to the high-pressure side and/or the low-pressure side of the refrigeration circuit.

The inventive method and apparatus for operating a refrigeration circuit as well as additional embodiments of the refrigeration circuit are described in greater detail in the following on the basis of the exemplary embodiment depicted in the FIGURE.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates an embodiment of a refrigeration circuit in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE DRAWING

The exemplary embodiment depicted in the FIGURE has five heat exchangers E1 through E5, a single-component or multi-component compressor unit V, a separator A, two expansion valves a and b, two expansion turbines X and X′, as well as lines 1 through 16 connecting the aforementioned components.

The indications of temperature, pressure and flow given as examples in the following apply to the design of the described refrigeration circuit as a pure nitrogen refrigeration circuit.

The heated refrigerant with a temperature of 80.8 K and under a pressure of 150 kPa is withdrawn from the separator A, via which a heat exchange takes place with a user-defined medium. The heat input in the separator A is 32 kW. The refrigerant is fed via the line sections 12 through 16 through the heat exchangers E4 through E1, and in the process heated to a temperature of 300 K. The refrigerant withdrawn from the separator A is heated in heat exchangers E4 through E1, which it flows through in succession, in the opposite direction of flow from the compressed refrigerant that is conveyed to heat exchangers E1 through E4 in line sections 3, 4, 9 and 10.

Before conveyance to the single-component or multi-component compressor unit V, the heated refrigerant has a pressure of 130 kPa. The refrigerant is compressed to the desired circuit end pressure of 1520 kPa in the compressor unit V.

The compressed refrigerant is then conveyed via line 1 to the heat exchanger E5, where extraction of the compression heat takes place in exchange for a suitable cooling medium, such as water, that is fed through heat exchanger E5 via line 2. The refrigerant exiting from the heat exchanger E5 has a temperature of 302 K. The flow volume is 828 g nitrogen per second.

After extraction of the compression heat in the heat exchanger E5, the compressed refrigerant is conveyed to heat exchanger E1 via line 3 and cooled down there against itself. After the heat exchanger E1, the refrigerant is separated into two refrigerant partial streams, wherein one partial stream is conveyed via line 4 to the heat exchanger E2, while the second partial stream is conveyed via line 5 to the first of two expansion turbines X and X′. The flow volume of the first refrigerant partial stream is 168 g nitrogen per second and the flow volume of the second refrigerant partial stream is 660 g nitrogen per second.

The aforementioned first refrigerant partial stream is further cooled down against itself in the heat exchanger E2 and then conveyed via lines 9 and 10 to heat exchangers E3 and E4 and also cooled down against itself in these heat exchangers. Lastly, this refrigerant partial stream is expanded in the separator A via the expansion valve b provided in the line 11.

The second refrigerant partial stream of the refrigerant withdrawn from the heat exchanger E1 is conveyed at a pressure of 1490 kPa and at a temperature of 130 K via line 5 to the first expansion turbine X. Expansion takes place here to an intermediate pressure of 532 kPa. The expanded refrigerant partial stream, which has a temperature of 99 K at the outlet from the expansion turbine X, is conveyed via line 6 to heat exchanger E3 and heated herein to a temperature of 111 K against the first to-be-cooled refrigerant partial stream, which is conveyed to the heat exchanger E3 via line 4.

The second refrigerant partial stream is then conveyed via line 7 to the second expansion turbine X′ (it has a pressure of 530 kPa at the inlet to the expansion turbine X′) and is expanded herein to the desired end pressure or low pressure of 150 kPa.

According to the invention, the two expansion turbines X and X′ are henceforth arranged in such a way that the temperature of the refrigerant at the exit of both expansion turbines X and X′ is above the saturation temperature. In this connection, the temperature of the refrigerant is less than 10° C., preferably less than 5° C., in particular less than 2° C., above the saturation temperature of the refrigerant.

Via line 8, the expanded refrigerant partial stream, which has a temperature of 82 K, is then added to the refrigerant partial stream withdrawn from separator A in line 12.

Two dashed lines 17 and 18 are depicted in the FIGURE, and a dashed control valve c or d is provided in each of these. These lines and control valves make it possible to connect the first expansion turbine X on the exit side to the high-pressure side and/or the low-pressure side of the refrigeration circuit.

The pressure between the expansion turbines X and X′ can be optimized in a comparatively simple manner by means of these lines and control valves such that the temperatures of the refrigerant (partial stream) 6 and 8 at the exits of both expansion turbines X and X′ are just above the saturation temperature of the refrigerant.

The control valve a depicted in line 5 is used to start and stop the expansion turbines X and X′ as well as to restrict the refrigerant stream conveyed in the expansion turbines X and X′ in the case of partial loads.

The inventive method and apparatus for operating a refrigeration circuit is suitable in particular for refrigeration circuits in which nitrogen or a nitrogenous refrigerant circulates.

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

1. A method for operating a refrigeration circuit, in which a single-component or multi-component refrigerant circulates, wherein at least one partial stream of the refrigerant is expanded, wherein the expansion of the at least one partial stream takes place in at least two expansion turbines that are arranged in series, and wherein a temperature of the refrigerant at an exit of the expansion turbines, or at least at one of the exits of the expansion turbines, is above a saturation temperature of the refrigerant.
 2. The method according to claim 1, wherein the temperature of the refrigerant at the exits of the expansion turbines, or at least at one of the exits of the expansion turbines, is less than 10° C. above the saturation temperature of the refrigerant.
 3. The method according to claim 1, wherein the temperature of the refrigerant at the exits of all the expansion turbines is above the saturation temperature of the refrigerant.
 4. The method according to claim 1, wherein an exit side of a first expansion turbine in a direction of flow is connected to a high-pressure side and/or a low-pressure side of the refrigeration circuit.
 5. The method according to claim 1, wherein the refrigerant is a nitrogenous refrigerant.
 6. The method according to claim 5, wherein the nitrogenous refrigerant is nitrogen.
 7. The method according to claim 2, wherein the temperature is less than 5° C. above the saturation temperature of the refrigerant.
 8. The method according to claim 2, wherein the temperature is less than 2° C. above the saturation temperature of the refrigerant.
 9. A refrigeration circuit, comprising: a low pressure side of the circuit; a high pressure side of the circuit; and a first expansion turbine and a second expansion turbine arranged in series, wherein a partial stream of a refrigerant on the high pressure side of the circuit is expanded in the first and second expansion turbines and wherein a temperature of the refrigerant at an exit of the first and second expansion turbines is above a saturation temperature of the refrigerant.
 10. The refrigeration circuit according to claim 9, wherein a second partial stream of the refrigerant on the high pressure side of the circuit is provided to a heat exchanger.
 11. The refrigeration circuit according to claim 10, wherein the partial stream of the refrigerant exits the first expansion turbine and is provided to the heat exchanger.
 12. The refrigeration circuit according to claim 11, wherein the partial stream of the refrigerant exits the heat exchanger and is provided to the second expansion turbine.
 13. The refrigeration circuit according to claim 12, wherein the partial stream of the refrigerant exits the second expansion turbine and is provided to the low pressure side of the circuit.
 14. The refrigeration circuit according to claim 11, wherein a portion of the partial stream of the refrigerant exiting the first expansion turbine is provided to the low pressure side of the circuit before the partial stream is provided to the heat exchanger.
 15. The refrigeration circuit according to claim 11, wherein a portion of the partial stream of the refrigerant exiting the first expansion turbine is provided to the high pressure side of the circuit before the partial stream is provided to the heat exchanger.
 16. A method of operating a refrigeration circuit, comprising: expanding a partial stream of a refrigerant on a high pressure side of the refrigeration circuit in a first expansion turbine and a second expansion turbine arranged in series, wherein a temperature of the refrigerant at an exit of the first and second expansion turbines is above a saturation temperature of the refrigerant.
 17. The method according to claim 16, further comprising providing a second partial stream of the refrigerant on the high pressure side of the refrigeration circuit to a heat exchanger.
 18. The method according to claim 17, further comprising providing the partial stream of the refrigerant exiting the first expansion turbine to the heat exchanger.
 19. The method according to claim 18, further comprising providing the partial stream of the refrigerant exiting the heat exchanger to the second expansion turbine.
 20. The method according to claim 19, further comprising providing the partial stream of the refrigerant exiting the second expansion turbine to the low pressure side of the refrigeration circuit. 